In present commercially marketed tractor operated hitches, a diagonal strut is pinned to a vertical strut and the vertical strut engages and supports a hitch head for holding a trailer kingpin in place on a railway flat car. A bumper block to be engaged by a tractor to collapse the hitch to a retracted position extends outwardly from the vertical strut in a direction away from the diagonal strut. However, connecting the diagonal strut to the vertical strut intermediate the length of the vertical strut introduces substantial bending loads into the vertical strut due to fore and aft movement of the trailer.
Because of these vending loads the vertical strut must be a heavy member, adding weight and expense to the hitch.
In one tractor operated hitch construction described in U.S. Pat. No. 3,202,390, the diagonal strut includes telescoping members held together by pins extending through the telescoping members. In order to collapse the hitch the operator manually removes the pins and then backs the tractor into the hitch until the hitch collapses. Thus the hitch is not truly automatic in that the operator must manually remove the pins prior to its collapse. In this regard this construction appears more dangerous than an automatic hitch knocked down by the tractor. Secondly, the hitch does not have a bumper block for the tractor to engage to collapse the hitch.
U.S. Pat. No. 3,228,641 discloses a tractor operated hitch in which a diagonal strut and a vertical strut are connected to the hitch head by two (2) common pins. However, the bumper block is connected to a separate vertical leg which is connected to the diagonal strut. This additional leg and its connections to the diagonal strut adds weight and expense to the hitch. Furthermore, the bumper block is located below the current industry standard covering the height of the bumper block, which requires the bumper block to be from 30 to 40 inches from the deck of the car.
If the diagonal strut and the vertical strut are both pinned to the hitch head, a problem exists as to how to mount the bumper block assembly on the hitch to comply with the industry standard concerning the height of the bumper block assembly in the upright position, and at the same time locate the bumper block assembly on the hitch such that when the hitch is in the retracted position on the deck, the bumper deck assembly does not project above the remainder of the hitch and thus complies with another industry standard which requires that no part of the hitch in the retracted position extend more than six (6) inches above the deck.
In U.S. Pat. No. 3,964,766, a trailer hitch is disclosed in which the vertical strut and the diagonal strut are both connected to the hitch head. However, in the description of the preferred embodiments, this patent refers to U.S. Pat. No. 3,493,207 for a description of collapsing the hitch to the deck of the car. This latter patent discloses a hitch in which the diagonal strut is pinned to the vertical strut rather than to the head. Therefore, U.S. Pat. No. 3,964,766 does not clearly teach tractor operation of a hitch in which the vertical strut and diagonal strut are connected to the hitch head and the operation thereof is clearly spelled out.